The present invention relates to a method for performing an elevator rescue run in an emergency situation, the elevator comprising an elevator car, a counterweight, a rope suspending the car and the counterweight, a drive motor, an emergency brake for stopping the car in an emergency situation and a motor drive unit for supplying drive power to and for controlling the drive motor, as well as a corresponding elevator.
For safety reasons elevators are constructed so as to immediately stop the the car in an emergency situation during its travel in the elevator shaft. Practically, power to the drive motor and the emergency brake is interrupted, causing the drive motor to stop driving the car and causing the emergency brake to fall in and to stop the car almost immediately. Since such stopping will normally not occur at a landing, but randomly at any location within the elevator shaft, passengers will get trapped in the elevator car. In such an emergency situation it is mandatory to free the passengers from the elevator car as soon as possible. This requires the presence of a technician or qualified personnel at the elevator site and it may take some time before such qualified person arrives.
In most cases the emergency situation is caused by a power failure in the main power supply to the elevator. Emergency situations may also be caused by defects in the elevator itself, for example an interruption of the safety chain, with the elevator control, the encoder, etc. While after a power failure the elevator takes up operation once power is again available, other situations require the presence of a qualified person as mentioned above.
There are two different emergency situations, i.e. an emergency situation in which car and counterweight are in an unbalanced condition, i.e. once the brake is lifted, the car starts moving by gravity. U.S. Pat. No. 6,196,355 B1 discloses an electrical elevator rescue system for freeing the passengers in this kind of situation. However, there also is the balanced load condition, i.e. even after lifting the brake the car will remain at its position. Due to the fact that normally elevators are designed to be in a balanced condition for the most common operational conditions, such a balanced load condition is not uncommon.
U.S. Pat. No. 5,821,476 teaches a carry-along emergency device including an emergency DC power supply, a switching device for alternatively feeding DC voltage for windings of the drive motor and an actuator for releasing the elevator brake. The switching device typically is a rotary switch having 6 contacts which are connected to the windings of the drive motor so that in the course of rotating the switch from one contact to the next contact the windings of the elevator motor are successively energized, thus advancing the car and the counterweight step by step.
Another approach for moving the elevator car in a balanced load condition is described in EP 0 733 577 A2, which suggests to provide a separate rescue drive means for moving the car in a balanced load condition.
The problem with any such construction resides in the fact that the respective methods of operation require the presence of a technician or a qualified person at the elevator site. Particularly, once such qualified person arrives at the elevator, he has to control the rescue run from a service panel board. The typical rescue operation is different for the balanced load condition and the unbalanced load condition. At the beginning, while monitoring the movement of the car, the technician will lift the emergency brake. To this effect normally the service panel board is typically provided with a “brake release button”. The technician will actuate the brake release button and, if the car is in an unbalanced load condition, the car will start moving. The technician will use the emergency brake for stopping the car, once the car has accelerated to a certain speed. By repeatedly opening and closing the emergency brake (“stutter braking”), due to gravity the car will move to an appropriate landing where the passengers may leave the car. If the car is in a balanced load condition, the car will not move, once the brake has been opened. In such a situation motive force to the car may be provided for example by the apparatus as described in U.S. Pat. No. 5,821,476 or U.S. Pat. No. 4,376,471.
The respective methods for performing the elevator rescue run of the prior art are complicated and require particular skills in for being performed.
It is therefore an object of the present invention to provide a method for performing an elevator rescue run which is simple and reliable.